Cytomegalovirus (CMV) disease is a relatively frequent, and often serious, complication in immunocompromised, CMV-infected patients. In the past few years, it has become apparent that to differentiate between subclinical viral shedding and large-scale viral replication, occurring during the prodrome before the onset of active disease, it is necessary to use sequential monitoring with a quantitative assay. Several studies have shown that CMV quantitative polymerase chain reaction (PCR) assays are more sensitive than buffy coat CMV antigen detection assays. This extra sensitivity can, in some cases, give an additional week of warning before the onset of CMV disease. Instituting antiviral therapy at an earlier time point in the prodromal stage may decrease the chance of the patient developing active CMV disease. We have completed development of a competitive quantitative PCR assay for the detection of CMV in buffy coat cells. The assay can detect as few as three to five viral genome equivalents in an amplification reaction tube. The coefficient of variance of this assay is about 40 percent, in line with other published descriptions of assays of this type. To have an assay with improved precision and, therefore, better potential predictive value for disease onset or progression, we have developed a real-time CMV PCR assay. This assay utilizes frequency resonance energy transfer fluorescence probes and is designed to run on the Roche LightCycler. Amplification and detection of the assay can be completed within 45 to 50 minutes. In addition to continuing the developmental work on a real-time PCR assay, we have begun performing an evaluation of the Organon Teknika NASBA pp67 CMV assay. This commercially available assay amplifies CMV RNA in an isothermal reaction using reverse transcriptase and RNA polymerase. A retrospective study was conducted comparing the performance of the real time quantatitive CMV PCR assay with the NASBA pp67 and pp65 antigen detection assays. The real-time CMV PCR assay was found to detect all the significant episodes of CMV viremia identified by the pp65 antigen assay, but also gave a positive signal at least a week earlier in about 75% of the episodes. The pp67 NASBA assay was less sensitive than the other two methods. These results were presented at the American Society for Microbiology meeting in May, 2001. We have initiated a prospective study utilizing the real-time CMV PCR assay to test whole blood samples from bone marrow transplant patients.